CD4+ T-lymphocytes and macrophages are the principal cellular reservoirs for primate lentivirus replication. However, there is a very limited understanding of processes influencing virus-macrophage interaction, nor is it clear as to the actual role played by the macrophage reservoir in viral replication. In the previous funding period we have garnered evidence to suggest that not only do macrophages provide conditions that may be highly advantageous for virus replication, but that the primate lentiviruses have evolved the ability to alter macrophage physiology in a way that enhances conditions for viral spread. These findings can be summarized as follows: 1. HIV-1, via the Nef protein, intersects the CD40 signaling pathway to promote the release of soluble factors that recruit T-cells to sites of viral replication and increase susceptibility of those cells to infection. 2. The ability of macrophages to sustain virus production requires induction of macrophage maintenance factors; an activity governed by the viral envelope glycoprotein. 3. HIV-1 assembles into cytoplasmic vesicles of infected macrophages. Virions within this compartment are highly stable and are transmitted to T-cells in trans. This points to a novel mechanism for viral persistence. In the next funding period we will define the biological significance of these activities in terms of viral replication and persistence in vitro and in vivo. Specifically, we propose to: AIM 1: Identify the mechanism by which primate lentiviruses intersect the CD40 signaling pathway in macrophages AIM 2: Define the mechanism by which HIV-1 induces macrophage maintenance factors and examine how they influence the outcome of the infection AIM 3: Characterize viral and cellular factors that influence the accumulation, stability and transmission of virions within cytoplasmic vesicles of infected macrophages. AIM 4: Examine in vivo characteristics of viruses altered in the ability to intersect CD40 signaling. These studies will define how macrophages contribute to primate lentiviral replication and pathogenicity and identify strategies through which to interrupt viral replication in this reservoir.